The present invention relates generally to a process for filtering engine exhaust and an engine exhaust filtering system. More particularly, this invention relates to an exhaust filtering system suited for use with diesel engines.
As concern for the environment increases, greater attention is being given to systems for eliminating damaging discharges from internal combustion engines. In the workplace, pollution created by combustion engines threatens the health of many workers, as the carbon contained in the exhaust may be carcinogenic. The problem is especially troublesome in enclosed environments such as warehouses or factories wherein diesel fork lifts are frequently used. Fork lifts are often operated in a cycling manner, that is, at maximum power for short spurts. At maximum power, the highest percentage of diesel particulate material is exhausted, exposing the operators to health risks. Thus, it can be seen that a system for reducing this harmful exhaust is needed. Prior filter units have generally been too expensive and difficult to service. In addition, prior filtering devices have not worked effectively during cycling when carbon exhaust is at a maximum.
The prior art, reflected by U.S. Pat. No. 3,738,089 to Brill, teaches an exhaust gas filter. Exhaust passes from the interior of a canister outward through a perforated wall and into a fiber blanket type filter medium located between the canister and a surrounding supporting shell and exits from openings at the rear of the device. A bypass valve opens to allow a direct passage of the exhaust gases through the canister and out to the atmosphere when the engine is under maximum power conditions so that the filter is ineffective in applications wherein the engine frequently cycles up to maximum power. Brill utilizes a deep pad type filter which clogs easily from diesel particulate material and is not easily cleanable.
In Mizrah et al., U.S. Pat. No. 4,732,594, there is described a process for scrubbing exhaust gases from diesel engines using an open pore ceramic foam filter. This type of filter requires temperatures above 550.degree. C., or temperatures above 400.degree. C. when the filter has a catalyst coating, to regenerate the filter by combusting the soot. In many applications, the filter will not reach the high temperatures required for regeneration so that a separate heat generation device must be added, thereby making the cost prohibitive.
In addition, the prior art also teaches several types of spark arresters generally located inside of a muffler to trap carbon particles.
None of the prior art devices adequately filter diesel particulate matter which is exhausted from diesel engines. The carbon particles in diesel exhaust collide and join each other to form larger clumps, having very low densities, on the order of 0.04-0.05 grams/cc. The dynamic equivalence, that is the solid particle that exhibits the same efficiency as the carbon clumps, is approximately 1.2 micrometers for diesel particulate matter. This microscopic size of the particulate matter makes filtering extremely difficult and containment and handling of the filtered material very burdensome.
The present invention addresses the problems associated with filtering exhaust from internal combustion engines. It is apparent that an improved system for filtering exhaust is needed for the health and safety of vehicle operators and those working nearby. The present invention solves these problems and others associated with filtering exhaust from diesel engines.